The Problem: Dual Writes

The last lesson named the dual-write problem. This lesson analyzes it in full. We will trace one operation as it fails in two different orders. Then we will see why the easy fixes do not work. By the end, we will know exactly what a real fix must guarantee.

What a Dual Write Is

A dual write is one logical operation that must change two independent systems. In our case, the two systems are the service's database and the message broker.

The database has transactions. The broker has its own delivery guarantees. **Neither system can join the other's transaction